University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications from the Harold W. Manter Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of 4-26-2001 Persistent Fontanelles in Rodent Skulls Scott Lyell Gardner University of Nebraska - Lincoln, [email protected] Sydney Anderson American Museum of Natural History Follow this and additional works at: https://digitalcommons.unl.edu/parasitologyfacpubs Part of the Parasitology Commons Gardner, Scott Lyell and Anderson, Sydney, "Persistent Fontanelles in Rodent Skulls" (2001). Faculty Publications from the Harold W. Manter Laboratory of Parasitology. 72. https://digitalcommons.unl.edu/parasitologyfacpubs/72 This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. AMNH NOVITATES Wednesday Jul 25 2001 01:36 PM 2000 novi 00211 Mp_1 Allen Press x DTPro System File # 01TQ PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3327, 15 pp., 8 ®gures, 1 table April 26, 2001 Persistent Fontanelles in Rodent Skulls SCOTT LYELL GARDNER1 AND SYDNEY ANDERSON2 ABSTRACT Persistent fenestrae occur between frontal or parietal bones in skulls of various rodents, especially species of Andinomys and Ctenomys. The frequency of occurrence and the shape and position of the fenestrae may vary with age or among individuals, populations, and species. Different families and species from both high and low elevations exhibit fenestrae. They have arisen in several different evolutionary lineages. Genetic factors contribute, but no clear func- tional signi®cance of the fenestrae has been established. INTRODUCTION years. These fenestrae occur in fewer taxo- Several years ago we noticed openings in nomic groups than do extra ossi®cations in the dorsal surface of various rodent skulls these sites. that we were collecting in Bolivia, usually We focus on the species of the genus Cten- between the frontals and/or parietals, specif- omys and on Bolivia. Selected material be- ically in Andinomys edax, a murid, and in yond this genus (phyllotines, octodontids, ca- more than one species of Ctenomys (®g. 1), viids) is included for comparison. The em- a caviomorph genus, from both the altiplano phasis on Bolivia is for the pragmatic reason and the lowland regions of Bolivia. that we were examining thousands of speci- Persistent fenestrae in fontanelle sites mens for a faunal study (Anderson, 1997). (openings that remain at an age when the Our goal here is to conduct a broad taxonom- openings in embryonic or infant braincases ic survey of midsagittal cranial fenestrae in between bones have closed in most other Bolivian rodents. mammals) or nearby sutures of rodent skulls We note that the presence of these fenes- have been noticed by a few workers over the trae was not noted by Hinton (1926) in his 1 Curator of Parasitology, Harold W. Manter Laboratory of Parasitology, University of Nebraska-Lincoln, Lincoln, NE 68588±0514. 2 Curator Emeritus, Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History. Copyright q American Museum of Natural History 2001 ISSN 0003-0082 / Price $2.00 AMNH NOVITATES Wednesday Jul 25 2001 01:36 PM 2000 novi 00211 Mp_2 Allen Press x DTPro System File # 01TQ 2 AMERICAN MUSEUM NOVITATES NO. 3327 classic book on the microtine rodents nor slit-like opening between the frontals at the have we found it in later reviews of the Ro- center of the interorbital region.'' Hershkov- dentia in general or in works dealing with itz (1962: 475) showed photographs of two cranial foramina in rodents (e.g., Hill, 1935; skulls of Andinomys with frontal fontanelles Wahlert et al., 1993). and wrote (p. 474) ``A slit-like fontanelle sometimes present between anterior halves of INSTITUTIONAL ABBREVIATIONS frontals. A second fontanelle sometimes pre- sent between posterior ends of frontals.'' AMNH American Museum of Natural History Also (p. 476), ``the interfrontal fontanelles BM British Museum (Natural History), now are larger and more consistently present in ``The Natural History Museum'', Lon- Andinomys than in other cricetines,'' and (p. don 477) ``Interfrontal fontanelles occur sporad- CBF ColeccioÂn Boliviana de Fauna, La Paz MNK Museo de Historia Natural ``Noel ically in a number of cricetines.'' Incomplete Kempff Mercado'', Santa Cruz de la fusion or apparent vascularization along the Sierra, Bolivia midline was noted in Andinomys and Ireno- MSB Museum of Southwestern Biology, mys by Steppan (1995: 33, 70, 92, 93). He University of New Mexico, Albuquer- noted (p. 33) that ``more than 90% of Andi- que nomys individuals examined (ø 50) possess MVZ Museum of Verebrate Zoology, Uni- a fontanelle, and several have a second fon- versity of California, Berkeley tanelle in the posterior region of the frontals MNHN MuseÂum National d'Histoire Naturelle, as well.'' Twenty-seven specimens were in Paris the list of specimens examined (p. 106). To Authors, authorities, dates, and references orient the reader, ®gure 1 shows the arrange- to sources of the scienti®c names used here ment of the bones in question in a complete may be found in Wilson and Reeder (1993), skull (®g. 1A) and a reduced drawing (®g. Anderson (1997), or Cook et al. (1990: 11). 1B) of the frontals, fenestra or fontanelle, Data on Ctenomys are summarized in table and parietals. The medial frontal sutures in I. We considered a table for other groups but four skulls of Andinomys are illustrated in decided that too many items needed quali®- ®gure 2. A slit-like fenestra, as noted by Os- cation. The great variability in size, shape, good and Hershkovitz, is present in three and position of fenestrae convinced us that it skulls. In the fourth skull there is no appre- was best to illustrate most individuals pos- ciable gap but the bones are unfused in four sessing the trait from various samples rather places. than trying to represent the variation by sta- Auliscomys (Loxodontomys, Mareso- tistics for measurements or just selected ex- mys).ÐHershkovitz (1962: 477) noted that treme conditions or ``typical'' individuals. interfrontal fontanelles ``are common, though Museum catalog numbers are given when we rarely well developed, in Phyllotis micro- think a future worker will need to examine pus'' [now placed in Auliscomys, e.g., Wil- the individual referred to. In other cases, col- son and Reeder (1993:695), or Loxodonto- lection locality and total number in the sam- mys, e.g., Steppan (1995: 106)]. We exam- ple will suf®ce to remove ambiguity. ined 14 A. micropus, 24 A. pictus, 61 A. sub- Statistical analyses were conducted using limis, and six A. boliviensis (the latter placed Systat 8.0. The interactions between preva- in the genus Maresomys by Braun, 1993). lence and altitude were analyzed using the Only one skull has a fenestra (®g. 2, A. mi- ANOVA function. Correlation coef®cients cropus, AMNH 14290, from Rio Chico, San- were generated using standard regression ta Cruz, Argentina). equations. Levels of statistical signi®cance Galenomys garleppi.ÐNone of the eight were set prior to all analyses at p # 0.05. skulls examined has an open fenestra. RESULTS Tapecomys primus.ÐTwo skulls of this phyllotine, from Tapecua, Tarija Department, MURIDAE,SIGMODONTINAE,PHYLLOTINI Bolivia (CBF 2414 and AMNH 264448) do Andinomys edax.ÐOsgood (1947: 173) not exhibit any sagittal fenestrae. wrote that ``in ten skulls examined there is a A skull of Punomys lemminus from Peru, AMNH NOVITATES Wednesday Jul 25 2001 01:36 PM 2000 novi 00211 Mp_3 Allen Press x DTPro System File # 01TQ 2001 GARDNER AND ANDERSON: RODENT SKULL FONTANELLES 3 of bone is usually visible through the gap. There is a thickening of the bone near the midsagittal line and often a shallow space within this thickening. Whether this is a si- nus or is occupied by a blood vessel or other tissue is not clear in the cleaned skulls. In a few cases, the opening is not underlain by other bone and extends into the braincase. For example, in specimen AMNH 231634 the anterior gap is completely open and the posterior gaps exhibit bone beneath them. OCTODONTIDAE Aconaemys fuscus.ÐThree (young adults) of 13 skulls (11 MVZ, 2 AMNH) from Ar- gentina have fenestrae. One (MVZ 163418) Fig. 1. A. Drawing of skull of Ctenomys sp., has a fenestra 2.1 by 0.5 mm, one (AMNH dorsal aspect with fenestra evident at junction of frontal and parietal bones. B. Dorsal aspect of 91654) is 2.5 by 0.3 mm, and one (AMNH only frontals and parietals showing relative rela- 91655) is 4 by 1 mm. Two other young in- tionship of bones as in ®gures 2±7. dividuals lack fenestrae. Octodon degus.ÐOne (MVZ 150081, a juvenile) of 21 skulls (5 AMNH, reared in ®gured by Pacheco and Patton (1995:89), the laboratory; and 16 MVZ, from 1000 m shows a slit-like opening between the fron- elevation in Chile) had a minute fenestra (2 tals in the region of the interorbital constric- by 0.5 mm). tion. Steppan (1995: 16) studied 12 speci- mens of P. lemminus and scored Punomys as Octodon lunatus.ÐTwo of 24 skulls (5 having ``partially open or vascularized'' me- AMNH, 19 MVZ) had a fenestra. These two diodorsal frontal sutures but no further de- animals were young, and the fenestrae were tails were provided. Punomys was assigned along the midsagittal line (AMNH 33275, to Phyllotini by Olds and Anderson (1990: 40075, 2 by 4 mm). All MVZ specimens 63), but Steppan (1995: 109) placed it incer- (from 1000 m in Chile) were adults and none tae sedis in Sigmodontinae. had fenestrae.